Microelectronic devices, such as monolithic integrated circuits (ICs), for example, may include a number of transistors, such as metal oxide semiconductor field effect transistors (MOSFETs) fabricated over a substrate, such as a silicon wafer. As device sizes continue to decrease, stacking of devices in a third dimension, typically referred to as vertical scaling, or three-dimensional (3D) integration, becomes a promising path toward greater device density.